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F. J. HOOVEN PHOTOTYPESE'I'TING 16 Sheets-Sheet 1 a, FREDERICK J. HOOVEN Gttomega Jan. 6, 1959 Original Filed Jan. 11 1951 31 ASA ERASER Jan. 6, 1959 HOOVEN Re. 24,584

PHQTOTYPESETTING Original Filed Jan. 11, 195] 16 Sheets-Sheet 2 fi +I5O 1312-4 soKg; 500K I AU? L5 I IOOAIF- 0 L OUTPUT .Olmf EEIOOK v .oI- 5E 55 F E II- AMPLIFIER I2AU7 INPUT -1 OUTPUT INPUT-2 K GATE iE' A-5OV INPUTS TO GATE OUTPUT FROM GATE 3, SEC.

I512- 8 NARROW PULSE NARROW PULSE 6AL5 INPUT-1 INPUT-2 I IE OUTPUT Zhwentor F a FREDERICK J. HOOVEN BUFFER WZMMQM attorney;

F. J. HOOVEN PHOTOTYPESETTING Jan. 6, 1959 16 Sheets-Sheet 5 Original Filed Jan. 11, 1951 60mm 39 mm zmao omdm 1:3 mm d 0 0253 .02- dmqm It; 5 0 mm 02-03402.

EP-.2300 umJDm u0 mm QZFZEA m0 mu -Z300 uwJDa uOSmw 02-260mm Nw hh mm mo mm oh PE; mm mo 6 20E FE;

FREDERICK J. HOOVEN mwlgjwa-bu attorneys Jan. 6, 1959 F. J. HOOVEN PHOTOTYPESETTING Original Filed Jan. 11, 1951' 16 Sh eets-Shet 6 FLASHING LIGHT CONTROL Snoenlor bin-viii FREDERICK J. 'HOOVEN M Gttgmegs STEP CONTROL Jan. 6, 1959 F. J. HOOVEN Re. 24,

PHOTOTYPESETTING Original Filed Jan. 11. 1951 W 16 Sheets-Sheet 7 3nnntor FREDERICK J. HOOVEN attorneys Jan. 6, 1959 F. J. HOOVEN Re. 24

PHOTOTYPESETTING Original Filed Jan. 11, 1951 16 Sheets-Sheet 8 3noentor FREDERICK J. HOOVEN attorneys Jan. 6, 1959 F. J. HOOVEN Re. 24,584

' PHOTOTYPESETTING I Original Filed Jan. 11, 1951 1e Sheets-Sheet 9 l lg-WA MEMORY IWORD w.s.s.s. :SPACE :szousuce :SELECTOR Inventor FREDERICK J. HOOVEN W WZ M attorneys Jan. 6, 1959 F. J. HOOVEN Re. 24,584

PHOTOTYPESETTING Original Filed Jan. 11', 1951 16 Sheets-Sheet 10 FLASH CHARACTER 160 LAMP SPACE PULSE 490 GENERATOR 3nvntor FREDERICK J. HOOVEN Jan. 6, 1959 F. J. HOOVEN PHOTIOVIYPESETTING Original Filed Jan. 11 1951 16 Sheets-Sheet 11 Jig-18 C HARACT ER DRUM CHA RACTER SPACE PULSE GENERATOR BOZ Snnentor FREDERICK J. HOOVEN WZWsrM attorneys Jan. 6, 1959 HQQVEN Re. 24,584

PHOTOTYPESETTING Original Filed Jan. 11, 195] 16 Sheets-Sheet l2 R.S.PC. S-' 1 RECORDING SEQUENCE SELECTOR R ss CHARACTE MEMORY CYLINDER Plg-ZO WORD SPACE SEQUENCE SELECTOR 3 nnentor FREDERICK J. HOOVEN mwyw Gltomeg:

Jan. 6, 1959 F. J. HOOVEN Re. 24,584

PHOTOTYPESETTING Original Filed Jan. 11. 1951 l6 Sheets-Sheet 13 C O 57 437 a17 I K 402,

SEQUENCE W555. SELECTOR FREDERICK J. HOOVEN Jan. 6, 1959 F. J. HOOVEN Re. 2

PHOTOTYPESETTING Original Filed Jan. 11. 1951 16 Sheets-Sheet 14 PSRC.

R e 0 c fig] 44Z\ I 485 V i I 472. A3 A6 A9 :1? m2 cHAR'AcTER DRUM c HA MEMORY YLINDE 0 a o a o 0 0 a o 460 I CHARACTER SPACE PULSE 130 GENERATOR PRINTING SEQUENCE SELECTOR 3nventor a; FREDERICK J. HOOV-EN attorneys Jan. 6, 1959 F. J. HOOVEN Re. 24,

PHOTOTYPESETTING Original Filed Jan. 11, 1951 16 Sheets-Sheet 15 *esnc. sac.

505 '-52s I 02 [I52 |aa 508 I I 89 810 s11 12 0 44Z\ 485 A A6 A9 CHARACTER MEMORY- CYLINDER Snventor FREDERICK J. HOOVEN (Iltomegs Jan. 6, 1959 F. J. HOOVEN Re. 24,

PHOTOTYPESETTING Original Filed Jan. 11. 1951 IG-Sheets-Sheet l6 Eng-24 RsPc.

A KERN 3 c L l 9/ i i 5 530. 530' 5z1531 5 531 Y 331 I I s] T L 54% szz 542 L MEMORY 145 CYLINDER 'CHARACTER SPACE PULSE cHARAcTER GENERATOR DRUM v Snventor FREDERICK J. HOOVEN attorney:

Unite States PHOTOTYPESETTING Frederick J. Heaven, Dayton, Ohio Original N0. 2,714,842,1lated August 9, 1955, No;

205,576, January 11, 1951. Application for November 26, 1956, Serial No. 624,481

41 Claims. (Cl. 95-4 .5)

reissue Matter enclosed in heavy brackets 1 appears in are original patent but forms no part of this reissue specification; matter-printed in italics indicates the additions made by reissue.

This invention relates to photographic type composition and more particularly to a system by means of .which text matter can be directly composed, letter by board in the ordinary manner, with the production ofthe typed or equivalent record by means of which the line may be checked for accuracy, following which upon the operation of a printing key, the machine will automatically print the line upon a film in selected typefaces, quickly and accurately, and accomplish the justification of the line in the process, the operator meanwhile continuing with the composition of a succeeding line.

It is a further object to provide such a machine in which the characters are arranged to be printed by a flashing light source which is. of sufficiently short duration that the character is selected while the system is in continuous rotation with the film being advanced in direct correlated relation therewith.

It is also an object to provide such a system in which the flashing of the light source takes place at a predetermined time during the revolution of the system to effect the flashing of the selected character and in which the system continues to rotate for a predetermined whole number of revolutions between successive characters with corresponding advance of the film to thereby obtain proper character spacing.

It is likewise an object to provide a system for selection of the desired characters and the, storing of data indication of both the selected character, its sequence in the line, and its width, and to control the flashing of the light source within a single revolution to elfect the selection of the characters in the desired sequence, and to delay the flashing while the rotation of the system is continued between successive llashings to effect the amount of film advance corresponding to the width of each'selected character; 1

It is a further object to provide for continuing the rotation of the system between the last character of one Word and the first character of the following word for an additional number of revolutions to effect continuous advance of the film, thereby forming spaces between the words.

It is also an object to provide for justifying the line by counting the total width of all the characters in the line, counting once during each revolution of the system thenumber of word spaces in the line, and repeating the count of the number of such word spaces with continued rotation of the system until the total count equals the maximum available width of the line with the film atnt ice continuing to advance and thus forming the word space, the system then'returning to the selection of characters.

It is a further object to provide such a system in which the same counting operations are repeated for each word space in the line. I i

It is also an object to provide a system in which are magnetically recorded in predetermined positions to effect selection of the desired'characters for printing and in which other pulses are magnetically recorded in predetermined numbers to control the width of the spaces between characters. g

It is likewise an object to provide a control by means of which the operator can depart from the standard I spacing which automatically occurs upon the selection of Inductance:

a character, and produce a non-standard spacing of a predetermined width, wherever such may be desired.

it is a still further object to provide a control by means of which the operator may efiect the kerning of vtwo adjacent characters by interrupting the standard spacing sequence and elfecting a selected lesser spacing.

Numerous other objects and advantages will be apparent from the following description, the accompanying drawings, and the appended claims.

Referring to the drawings, they are largely diagrammatic and simplified in order to enable the principles of the invention to be more'readily understood, and in some cases such as in the circuit diagrams, only a limited number of character bars and selection circuits are illustrated since they are adequately illustrative of the remainder of the system and to include the entire circuits would greatly complicate and interfere with the ease of understanding the invention. Also, a number of elements are shown fully as such, and thereafter are indicated diav I grammatically as they appear in the complete circuit.

The diagrams carry identifying data with regard to typical components including values of voltage, resistance, capacitance, inductance, and further identify electronic tubes suitable for the purposes by their common commercial designations, the purpose'being to enable one skilled in the art to understand and to be able to reconstruct the apparatus in accordance with the teachings contained herein but not to limit the invention to any such specific data, etc; .Throughout the diagrams the following designations have been used'in accordance with conventional practice.

Resistance:

K1,000 ohms M1,000,000 ohms Capacitance: I

uf.,microfarads an or tf.micromicrofarads mh. rnillihenries Fig 3 is a diagrammatic view of a typical circuit for the erasing heads;

Fig. 4 shows a typical circuit for the amplifiers designated in the system as A1, A2, etc. circuit diagrams which follow, all Amplifiers, Gates and Bufiers are shown with the input at the bottom designated by an arrow and the output at the top;

Reissued Jan. 6, 1959 I pulses I In the simplified and for kerning.

Fig. 5 shows a typical circuit for the gates, similarly designated in the system; I

Figs. 6 and 7 show the relationship of the broad and narrow pulses which are utilized in the operation of the' gates in the system; v F g. 8 is a typical circuit diagram of the buffer circuits; F1g. 9 1s a view of a trigger or flip-flop circuit, shown as the Eccles-Iordan trigger circuit which is used in comand the opening pulse, designated as 0, comes in at theright. Neither of these pulses appears in the output circult, and a pulse appears in the output in the event one appears at the input only if the switch is closed. When the switch opens, it generates a pulse which appears in the output circuit indicated by a'downwardly directed arrow at the lower right; v

Fig. 11 is'a schematic showing of a portion of the circuits for the space register counter, the actual counter having a larger number of stages, such as 10, with the intermediate stages included between the dotted line break being in all respects similar to those shown;

Fig. 12 is a view showing the circuit for the recording space pulse counter, hereinafter referred to as the RSPC, and since this counter is essentially the same as the printing space pulse counter, PSPC, it also serves to illustrate the circuit for the latter, the several input and output connections being suitably designated for the respective counters;

Fig. 13 is a diagrammatic view showing the circuits for the flashing light control;

Fig. 14 is a combined schematic and diagrammatic view showing the mechanism for advancing the recording apparatus in step by step movements as-the selection of the characters takes place; I A,

Fig. 15 is a schematic view in perspective of the-mechanism for selecting the desired font andpoint size, and the film advance andtraverse mechanism;

- Fig. 16 is a diagram showing the control for the film advance;

Figs. 17A and 1713 when taken together form an overall circuit diagramillustrative of the operation of the system but limited, for purposes of better understanding, to include only 12 character selections;

Fig. 18 is a schematic diagram of the portion of the circuits employed in the initial selection of characters;

Fig. 19 is a circuit diagram of the portions of the circuits utilized in recording a sequence of the characters and obtaining the count in the recording space pulse counter corresponding to the width of each selected character in terms of pulses;

Fig. 20 is a circuit diagram showing the controls which are operated upon the actuation of the word space bar; Fig. 21 is a schematic view of certain of the circuits which are operated upon the closing of the print key;

Fig. 22 is a schematic view of the circuits for printing and flashing the characters in the selected sequence;

Fig. 23 is a circuit view showing the connections for the counters which accomplish the justification of the line; and

Fig. 24 is a circuit view showingthe circuits which are utilized to effect non-standard spacing of the characters,

. The term film" is used herein comprehensively to avoid the necessity for repeating the various types of record materials which can be used, such term'being intended to include all light-sensitive or radiation sensitive sheet or web materials suitable for the purpose; similarly the term photographidand its'several variations are intended to include the correspondingmeans or method for producing the latent image thereon.

' symbols.

GENERAL DESCRIPTION With the machine of this invention the operator sits at a keyboard such as that of a typewriter or a similar board'having a larger number of characters, the operation being essentially normal in that the line is typed and a typed copy appears in front of the operator for checking purposes. Alternatively the keyboard or its equivalent may be actuated automatically from a previously prepared record in the form of a tape, Wire recording other suitable record. During this operation the machine stores the pulse data for character selection and spacingby means of magnetic recording generally similar to the recording of sound on tape or otherwise. Preferably the pulses are recorded on discs or cylinders which are mounted on the same shaft asthe character drumand'thus form part of the rotating system. In this way the entire system is self-synchronous and the exact speed or variations of speed at which it may operate are relatively unimportant.

The magnetic method of registering or recording such data is equivalent to memorizing the same and has the advantage that the data can be erased at the end ofthe cycle and new data recorded. Furthermore the system operates without physical contact, thus eliminating the Wearing characteristics of brushes, contactors or like. mechanical means. After the operator has completed a line and checked it for accuracy, he operates a control. such as a Print Key which sets in motion the automatic printing cycle and the machine then justifies and prints the line while the operator is composing a new line.

The machine is provided with a character carrier in the form of a master stencil or the like carrying the characters as transparencies and arranged for continuous relative rotation with respect to a flashing light source of extremely short duration. and as a preferred embodiment the character carrier is in the form of a drum on the rim of which the characters are carried and rotated continuously and at high speed past the stationary light source which may be a gas discharge lamp or spark. Both the lamp and spark give a flash of light of high intensity and extremely brief duration, as required to elfect the flashing of the selected character without blurring. I I c The film also moves in translation in a continuous predetermined fixed relation with the rotation of the drum, as distinguished from an intermittent travel between successive flashings of the selected characters, and preferably in the direction tangent to the rotation of the drum. The characters are arranged in a single row on the stencil up to the maximum number in any one font, such as approaching 120, including all three cases with special Different fonts are arranged in other axially spaced rows on the drum and arranged tobe brought selectively into proper flashing relation with the film by suitable manual or automatic controls and adjustments. The character drum, the moving film and the several magnetic recording discs as hereinafter described thus constitute a continuously rotating,"self-synchronous system.

As a result of the fixed relation between the rotation of the character carrier and the continuous translation of the film, the smallest increment of character space meas urement permitted by the machine is the distance traveled by the film in one revolution of the drum. For con venience, this space is referred to throughout as an iota, or an i. By suitable change in the ratio between the rotation of the character drum and the amount of film advance, provision is made for varying the linear dimensions of this unit, as may be desired for diiferent fonts and point sizes of type, a suitable relation being about 8 i per cm. v 7

Assuming a datum line on the rotating character drum to be considered as the zero angle position, the projection of this line on the film for each drum revolution would be the mark of the i space, and each character on the For purposes of illustration drum will be printed with a fixed relation to this line regardless of its angular position on the drum. This is accomplished by having each character slightly displaced from the optical axis at the instant of the flash, this displacement being proportional to the angular position of the character on the drum.

It will thus be seen that character selection is measured in fractional portions of a single revolution, that is, by determining the precise instant in the revolution at which the flashing of the light source occurs. Character spacing, on the other hand, is measured in whole revolutions of the system, there being a predetermined number of complete revolutions of the system for each character, depending upon the width or number of space units of that character. The system proceeds to the selection of the next succeeding character only after the completion of the desired number of full revolutions, and thus each character is properly selected and the film properly advances in proportion to the width of that character while the entire system is in continuous rotation.

Similarly when a word space occurs the system provides for continuance of the rotation of the system for a larger number of complete revolutions, thereby advancing the film by a greater amount before returning to its character selecting function, thus forming a space between the last character of one word and the first character of the next word in the line.

In order to accomplish such justification or composition of equal length lines of type, the length of each word space is determined by suspending the process of printing and spacing of characters and the following operation is performed whenever a word space occurs: The total number of spaces occupied by all the previously recorded characters of the line is counted once, then the total number of word spaces (which has been previously recorded) is counted repeatedly, once during each revolution of the system until the total count equals the predetermined total available space in the line. This total count will usually not coincide exactly with a complete number of revolutions and thus will be reached during one revolution of the system, and character printing will be resumed at the end of this revolution. As the total count is exceeded during the completion of this revolution the excess count is retained until the next succeeding word space occurs and the count which takes place at that time starts with this initial count. The same complete operation of counting character and Word spaces takes place upon the occurrence of each word space and in this way the line is justified for printing.

The maximum speed of the machine is determined by the maximum permissible speed of the character drum, this being established by the duration of the light flash during the exposure. A speed of 60 revolutions per second gives a printing speed of 60 i per second, equivalent for example to 7 /2 ems per second, or an average of about characters per second.

The system utilizes electronic control circuits and they I are primarily arranged so that they do not require proportional or variable control, but are actuated only into the On or Off position, where they are either conducting or non-conducting. This provides for a high degree of reliability and accuracy, as well as assuring such operating conditions under extremely high speed operation.

The electronic mechanisms are largely operated by and are used to produce electronic pulses. A pulse is here defined as a brief duration of current or voltage in a circuit otherwise not energized. In the present system the pulse is not measured quantitatively but merely its presence or absence is utilized to control the electronic mechanisms. All operating data for the machine is translated into pulses which by their number and timing establish the timing of the light flash within a single revolution and with the proper interval to allow a definite whole number of revolutions of the system which determines the selection and the spacing of the printed characters.

Controls are also provided by means of which the operator can dispense with the normal spacing procedure and provide for the insertion of a non-standard spacing of a predetermined width. Likewise a kerning control is located on the keyboard and by operation of this control concurrently with the actuation of a character key, the normal spacing procedure is interrupted and the operator can then actuate one of the selective space keys to produce a predetermined lesser space than normal for such character, thereby accomplishing kerning, the system returning to normal operation upon release of the kerning control.

DESCRIPTION OF ELEMENTS Magnetic recording, pick-up and erasing heads In Fig. l is shown the magnetic head used for mag-' netic recording, pick-up, and erasing. This head is generally similar to those widely used in the magnetic recording of sound on wire and tape with modifications necessary for the handling of higher frequencies. Referring to Fig. 2 there is shown a laminated magnetic core structure 10 in which there is incorporated an air gap 11 which is of the order of .003 inch. The core structure is held in close proximity to a rotating disc or drum 12 of nonmagnetic material such as bronze which is covered with a thin coating of magnetic material 13 which may be finely divided iron oxide powder with a suitable binding agent or a thin electroplated coating of iron of the order of thickness of the coating of .0002 inch. The magnetic core 10 is Wound with two coils of fine wire 15 and 16 which are shown connected in series to terminals 17 and 18. In operation when a current is passed through coils 15 and 16 magnetic flux is caused to flow in core 10 and because of the magnetic reluctance of gap 11 some of this magnetic flux flows through magnetic material 13 in completing the magnetic circuit. This results in the creation of permanent magnetic poles in the magnetic coating 13.

During subsequent operation whenever one of these poles passes the gap 11 a voltage will be generated in the coils 15 and 16 generating a pulse of voltage of wave form generally similar to the impressed current of the recording process above described. As an example, drum 12 may have a circumference of 24 inches and rotate at a speed of 60 revolutions per second. The linear speed of the coated surface past the magnetic gap will be then feet per second. It has been found practicable to record as many as 1000 separate such magnetic poles per foot by these methods and it is therefore practicable to record 120,000 distinct pulses per second. By passing a direct current through the coils 15 and 16 in the opposite direction from that normally used in the recording of pulses it is possible to magnetize the material 13 to the point of saturation which wipes out all previously recorded magnetic poles and thereby erases the recorded pulses and leaves the magnetic circuit ready to receive newly recorded pulses. In the following circuit diagrams the magnetic head generally described above and shown in Fig. 1 incorporating power supplies and amplifying circuits as described hereinafter is represented by the three different symbols shown as part of the figure for the several different purposes of recording, pick-up, and erasing.

With general reference to the electronic circuit diagrams referred to hereinafter certain simplifying conventions of representation have been adopted. All tube types are labeled by the commercial designation commonly used by those skilled in the art and by means of which they may be readily identified. All these tubes are of the general type having indirectly heated cathodes, the cathode heaters with their associated circuit and sources of power having been omitted for the. sake of clearness. Likewise sources of plate and bias potential have been indicated in all cases by external characters marked for example and -50, it being understood that these voltages are referred to ground potentials and represent any suitable source of direct current, one of whose supply terminals is connected to ground All input and output circuits are likewise returned to ground and when in the unexcited condition will rest at ground potential. All pulses impressed on such in put and output circuits consist of short application of negative potential of the order of, for example, 10 volts. Typical pulse wave forms are shown in Fig s. 6 and 7 and will, except where noted, have the forin' shown in Fig. 7, the duration of which is about 3 microseconds i Y Referring to Fig. 2 this will be re cognized as a two stage amplifier. This amplifier is adapted to respond only to negative pulses, and to that end the circuit is designed so that the input grid G11- of tube V1 operates at a slight positive potential with respect to cathode K11 of tube V1 since K11 is maintained at a negative potential with respect to ground, and current will flow through resistance R1, and from G11 to K11. Under these conditions a relatively large current will flowthroug h R2 and from P11 to K11. The resultant potential across R2 causes a negative bias on grid G21 of tube V2 such that no plate current flows in tube V2. When a negative pulse is impressed on gridG11 the current through R2 is cut otf, and'this removes the negative bias on grid G21, which allows the flow of current in the circuit consisting of L1, C1 and coils 1'5, 16 of the magnetic recorder head.

Erasing may be accomplished by discharging a condenser through a typical magnetic head such as shown in Fig. l. The erasing head may be the same type head as that used for recording and reproducing, but it is preferably wound with a larger number of turns of smaller wire. The discharge of a condenser through the head provides a convenient method of supplying a flow of current of known amount and duration, and

in addition provides the desirable characteristic of a current which diminishes smoothly from its maximum initial value to a suitably low value in a known time interval, and thus eliminates the risk of recording an undesirable transient on the magnetic medium when the circuit through the head is opened after erasing.

Fig. 3 shows a circuit adapted to energize an erasing head either by means of the momentary closing of a switch, or by means of a pulse. Condenser 20 is normally maintained in a charged state by a connection to the voltage source through resistor 21. Relay 22, having contactor 23 which is closed when the relay is energized, is connected in series with erasing head coil 24 and contactor 23, such that when contactor 23 is closed, a circuit is established whereby'condenser 20 is discharged to ground through coil'24, and relay 22. Switch 25 is connected across contactor 23, so that when switch 25 is closed thddischarge current flows. The flow of current energizes relay 22,'and closes contactor 23, so that the flow of current continues without regard to the further state of switch 25. When the current has decreased to a value less than that required to hold in relay 22, contactor 23 opens. Condenser 20 is so proportioned with respect to the combined resistances of coil 24 and relay 22 that the duration of current flow is substantially greater than the time required for one revolution of the system. If switch 25 has been opened previously, the discharge current then ceases, and condenser 20 recharges through resistor 21. If switch 25 remains closed, the current continues until switch 25 is opened, at which time condenser 20 is recharged.

Gas discharge tube is also shown, with its anodecathode circuit connected in parallel to switch 25. When a pulse appears on input terminal 31, the tube is caused to conduct, thus performing the same initiating function as described for switch 25. It will be apparent that either switch 25 or tube 30 may be used without the other or both may be used together, the switch being best adapted for initiationfr'om a mechanicaloperation,

and the tube being, adapted for pulse initiation.

For pick-up purposes, a magnetic head such as that tit) shown in Fig. l is used, one of the terminals 17 being connected to ground and the other teminal 18. being connected to transmit the induced pick-up 'pulseinto the amplifying and control system.

Amplifiers Referring to Fig. 4 there is shown the circuit for an amplifier such as represented in the schematic diagram Figs. 17A and 173 as A1, A2, etc. Without detailed discussion the 6AKS tube and associated circuit components will be recognized as a conventional pentode amplifier whose grid circuit is connected to a magnetic pick-up 40. The output of the 6AKS tube is coupled to the gird of one section of the double triode tube .12AU7. The first section of the 12AU'Z tube is connected as a cathode follower. The second section of the l2AU7 tube with plate and grid tied together functions as a diode rectifier whose cathode is directly connected to the cathode of the first section. The two cathodes of the 12AU7 tube will normally rest at a potential of about 3 volts positive and as a consequence there is normally no current flowing from cathode to anode of the second section. The magnetic pick-up 40 is so con.- nected to the 6AK5 tube that recorded pulses will impress positive potential on the grid of this tube. recorded pulses impressed on this tube will cause negative pulses to appear on the plate of the 6AK5 and'on the associated grid of the third section of the 12AU7. Such a negative pulse will impress negative pulses on the common cathodes of the 12AU7. Whenever the cathode of the second section of the 1'2AU7. becomes negative with respect to ground, current will flow to the anode of this section and through the 1K resistance to,

which the anode is connected and a negative pulse will thereby be impressed on the associated output circuit.

Since the normal potential of the 12AU7 cathodes is somewhat positive, it will be seen that any signal whose voltage is smaller that the amount of this positive bias will not pass through the associated rectifier circuit at all nor will any positive pulses pass through this circuit. As a consequence low-level background signals and undesirable hash will not be transmitted.

Gates In Fig. 5 is shown a gate circuit which may be defined as an element having two input circuits and one outputv circuit in which there is no output signal unless signals are simultaneously impressed on both input circuits. The l2AU7 tube shown has both cathodes and both plates connected in parallel in the form of a cathode follower with each grid'being connected to a separate input circuit. it will be recognized that both grids rest at ground potential and the cathodes will rest at a small positive potential as above described. it a negative potential is impressed on either grid along current will be main tained in the other section of the tube and the cathode potential wiil remain substantially unchanged. If however, a negative potential is impressed onboth grids, the potential of the cathode will then be correspondingly negative. The 6AL5 tube shown in Fig. 5 is a diode rectifier whose connections and functions are like those described in connection with the second section of the l2AU7 tube shown in Fig. 4.

The gate is used in order to assure that an output pulse will occur only when two input pulses are received either simultaneously or in overlapping relationship. It also serves to provide for accurate timing of the output pulse, this being illustrated in Figs. 6 and 7 where one input pulse is represented as a broad and the other as a narrow pulse. The. broad pulse in the condition shown in Fig. 6 is first impressed upon one input of the gate but no output pulse is produced until the later narrow pulse is received, and while the first pulse conditions the gate,

at which the gate becomes conducting and transmits its Thus. 

